Dielectric fluids

1. An ester composition, wherein the ester composition comprises esters formed from the reaction of:

(a) pentaerythritol; and

(b) three or more C 4 to C 12 monocarboxylic acids, wherein only one of the three or more C 4 to C 12 monocarboxylic acids is a branched carboxylic acid and the remaining acids are each independently linear chain carboxylic acids, wherein the branched carboxylic acid is selected from the group consisting of:

(i) a branched C 8 to C 12 carboxylic acid wherein the branched C 8 to C 12 carboxylic acid comprises a backbone having no branching at the C2 position; and

(ii) a branched C 9 to C 12 carboxylic acid wherein the branched C 9 to C 12 carboxylic acid comprises a backbone having branching at the C3 position; wherein the three or more C 4 to C 12 monocarboxylic acids comprise at least 50% of heptanoic acid, as a molar percentage of total acid content.

2. The ester composition of claim 1 , wherein the linear chain carboxylic acids comprise a linear C 10 carboxylic acid.

3. The ester composition of claim 1 , wherein the ester composition comprises esters formed from the reaction of:

(a) pentaerythritol; and

(b) four C 7 to C 10 monocarboxylic acids wherein at least one of the four C 7 to C 10 monocarboxylic acids is a branched C 8 to C 10 carboxylic acid wherein the branched C 8 to C 10 carboxylic acid comprises a backbone having no branching at the C2 position.

4. The ester composition of claim 1 , wherein the ester composition comprises esters formed from the reaction of:

(a) pentaerythritol; and

(b) heptanoic acid, n-octanoic acid, 3,5,5-trimethylhexanoic acid and n-decanoic acid; and

wherein the ester composition is prepared by reacting pentaerythritol with an acid mixture, wherein the acid mixture comprises heptanoic acid, n-octanoic acid, 3,5,5-trimethylhexanoic acid and n-decanoic acid in the following molar percentages of the acid mixture:

60-70% heptanoic acid;

12-20% of a mixture of n-octanoic and n-decanoic acids; and

15-25% 3,5,5-trimethylhexanoic acid.

5. A dielectric fluid composition comprising:

(I) an ester composition, wherein the ester composition comprises esters of:

(a) pentaerythritol; and

(b) three or more C 4 to C 12 monocarboxylic acids, wherein only one of the three or more C 4 to C 12 monocarboxylic acids is a branched carboxylic acid and the remaining acids are each independently linear chain carboxylic acids, wherein the branched carboxylic acid is selected from the group consisting of:

(i) a branched C 8 to C 12 carboxylic acid wherein the branched C 8 to C 12 carboxylic acid comprises a backbone having no branching at the C2 position; and

(ii) a branched C 9 to C 12 carboxylic acid wherein the branched C 9 to C 12 carboxylic acid comprises a backbone having branching at the C3 position;

wherein the three or more C 4 to C 12 monocarboxylic acids comprise at least 50% of heptanoic acid, as a molar percentage of total acid content; and

(II) one or more additives.

6. The dielectric fluid composition of claim 5 , wherein the one or more additives (II) are selected from the group consisting of antioxidants, metal deactivators and pour point depressants.

7. The dielectric fluid composition of claim 5 , wherein the dielectric fluid composition comprises an antioxidant in an amount of at least 0.0001% by weight of the composition and/or a metal deactivator in an amount of at least 0.0001% by weight of the composition; wherein the antioxidant optionally comprises a sterically hindered phenolic antioxidant and/or wherein the metal deactivator comprises a tolutriazole derivative.

8. The dielectric fluid composition of claim 5 , wherein the ester composition (I) comprises esters of:

(a) pentaerythritol; and

(b) heptanoic acid, n-octanoic acid, 3,5,5-trimethylhexanoic acid and n-decanoic acid; and

wherein the ester composition is prepared by reacting pentaerythritol with an acid mixture, wherein the acid mixture comprises heptanoic acid, n-octanoic acid, 3,5,5-trimethylhexanoic acid and n-decanoic acid in the following molar percentages of the acid mixture:

60-70% heptanoic acid;

12-20% of a mixture of n-octanoic and n-decanoic acids; and

15-25% 3,5,5-trimethylhexanoic acid.

9. A method of manufacturing an ester composition, wherein the method comprises forming esters by reacting:

(a) pentaerythritol; and

(b) three or more C 4 to C 12 monocarboxylic acids, wherein only one of the three or more C 4 to C 12 monocarboxylic acids is a branched carboxylic acid and the remaining acids are each independently linear chain carboxylic acids, wherein the branched carboxylic acid is selected from the group consisting of:

(i) a branched C 8 to C 12 carboxylic acid wherein the branched C 8 to C 12 carboxylic acid comprises a backbone having no branching at the C2 position; and

(ii) a branched C 9 to C 12 carboxylic acid wherein the branched C 9 to C 12 carboxylic acid comprises a backbone having branching at the C3 position;

wherein the three or more C 4 to C 12 monocarboxylic acids comprise at least 50% of heptanoic acid, as a molar percentage of total acid content.

10. The method of claim 9 , wherein the method comprises forming esters by reacting pentaerythritol with an acid mixture, wherein the acid mixture comprises:

50-70% of heptanoic acid as a molar percentage of the acid mixture; and

10-30% of a combination of C 8 and C 10 monocarboxylic acids as a molar percentage of the acid mixture and/or 10-30% of a C 9 monocarboxylic acid as a molar percentage of the acid mixture.

11. The method of claim 9 , wherein the method comprises forming esters by reacting:

(a) pentaerythritol; and

(b) four C 7 to C 10 monocarboxylic acids wherein one of the four C 7 to C 10 monocarboxylic acids is a branched C 8 to C 10 carboxylic acid wherein the branched C 8 to C 10 carboxylic acid comprises a backbone having no branching at the C2 position and the remaining carboxylic acids are each independently linear chain carboxylic acids.

12. The method of claim 11 , wherein the method comprises forming esters by reacting pentaerythritol with an acid mixture, wherein the acid mixture comprises heptanoic acid, n-octanoic acid, 3,5,5-trimethylhexanoic acid and n-decanoic acid in the following molar percentages of the acid mixture:

60-70% heptanoic acid;

12-20% of a mixture of n-octanoic and n-decanoic acids; and

15-25% 3,5,5-trimethylhexanoic acid.

13. A method of manufacturing a dielectric fluid composition comprising an ester composition, wherein the method comprises combining ester composition (I) with one or more additives (II) wherein ester composition (I) comprises an ester of:

(a) pentaerythritol; and

(b) three or more C 4 to C 12 monocarboxylic acids, wherein only one of the three or more C 4 to C 12 monocarboxylic acids is a branched carboxylic acid and the remaining acids are each independently linear chain carboxylic acids, wherein the branched carboxylic acid is selected from the group consisting of:

(i) a branched C 8 to C 12 carboxylic acid wherein the branched C 8 to C 12 carboxylic acid comprises a backbone having no branching at the C2 position; and

(ii) a branched C 9 to C 12 carboxylic acid wherein the branched C 9 to C 12 carboxylic acid comprises a backbone having branching at the C3 position; wherein the three or more C 4 to C 12 monocarboxylic acids comprise at least 50% of heptanoic acid, as a molar percentage of total acid content.

14. An electrical apparatus comprising the ester composition of claim 1 .

15. The electrical apparatus of claim 14 , wherein the electrical apparatus is a transformer.

16. A method of using the ester composition of claim 1 , comprising preparing a dielectric fluid comprising the ester composition of claim 1 and one or more additives, and introducing the dielectric fluid into an electrical apparatus.

17. The method of claim 16 , wherein the electrical apparatus is a transformer.